1. Field of the Invention
This invention relates to a method of manufacturing a thin film magnetic head. Thin film magnetic heads are used in a magnetic disc drives and magneto-optical disc drives.
2. Description of Related Art
Thin film magnetic heads are manufactured in a manner similar to a semiconductor integrated circuit elements, by film forming techniques such as vapor deposition, sputtering or the like or lithography such as photoengraving processes, etching, etc. These methods are advantageous in producing high-accuracy heads in large quantities.
There are two types of thin film magnetic heads hitherto known, i.e., a vertical head wherein a magnetic gap is formed in a direction perpendicular to a substrate surface (film thickness direction) and a horizontal head wherein a magnetic gap is formed along the substrate surface.
The vertical head is put to practical use because in the process of making vertical heads, it is easy to form a gap and vertical heads exhibit resistance against the sliding movement of a medium. On the other hand, the horizontal head makes it possible to complete whole processes, such as air bearing surface processing, in a substrate, since the surface of the head normally oriented to the medium is on the substrate side. Moreover, the depth of the magnetic gap is determined by the thickness of the film in the horizontal head, so that the depth of the gap is easily controlled during manufacture.
The procedures are generally carried out independently in the individual vertical head after the head is cut and separated from the substrate. Performing such procedures on individual vertical heads makes such heads more expensive generally than horizontal heads.
FIG. 1 is a cross sectional view depicting a horizontal thin film magnetic head described in "A NEW APPROACH TO MAKING THIN FILM HEAD SLIDER DEVICES" by IBM at IEEE INTEGRAM '89. As illustrated in FIG. 1, the thin film slider is comprised of the following elements: substrate 1, a protecting film 2, a magnetic gap 3, a lower magnetic core 4, an insulating layer 5, a coil 6, an upper magnetic core 7, a coil leading conductor 8, an insulative protecting film 9, a slider wafer 10 and a connecting conductor 11. The connecting connector 11 is within the slider wafer 10. The protecting film 2 protects the magnetic gap 3 and lower magnetic core 4 from sliding motions.
The manufacturing method and operation of the head shown in FIG. 1 will be described below.
First, the protecting film 2, comprising a metallic film and as a plating substrate, and the magnetic gap 3 are formed on the substrate 1. The magnetic gap 3 is formed with a submicron width through electron beam exposure. The gap is completed by the resist, or by etching a preformed a gap film (generally, inorganic insulative film) on the substrate using the resist as a mask.
A narrow gap width is considerably important to enhance the linear density in magnetic recording. It is thus required to form the pattern with a submicron width.
Next, the lower magnetic core 4 is formed through plating. At this time, the magnetic film is not formed on the part of the magnetic gap having the resist or insulative film. The insulating layer 5, coil 6, upper magnetic core 7 and coil leading conductor 8 are sequentially formed on the lower magnetic core 4 by films and lithography.
Then, the insulative protecting layer 9 is laminated and ground until a connecting part of the coil leading conductor 8 is exposed. The slider wafer 10 is bonded which serves not only to connect the coil terminals to the outside but to support the head elements.
Thereafter, the substrate 1 is dissolved through etching and removed, whereby the magnetic gap surface is exposed. The exposed surface is photoengraved and processed with a facing by ion beams or the like (to form an air bearing surface in a hard disc head).
The above-discussed method has such advantages that the gap of a submicron width is easily formed on a surface because the surface is flat and eventually the gap surface is made flat, and facing process of the head surface can be processed simultaneously for every substrate including several hundred heads without being separated into individual heads.
In the conventional manufacturing method of the thin film magnetic head, it is necessary to dissolve the substrate through etching, and therefore the material for the substrate is limited to one that can be etched. Moreover, it takes a long time to dissolve the substrate through etching. In addition, the substrate cannot be recycled, thereby causing a waste of resources and additional expense.
For example, in the case where Si of 4 inch diameter is used as the substrate, it should be 0.6 mm thick or so from the viewpoint of the strength, and not shorter than several hours is required to dissolve the substrate in a solution of sodium hydroxide.
Si substrate is not suitable in some cases since the coefficient of linear expansion thereof is smaller as compared with that of a magnetic film generally used in the magnetic core (it is desirable that the coefficient of linear expansion of the substrate in a thin film laminated body such as a thin film magnetic head is close to that of the magnetic film). Even if the other material is selected for the substrate, the material is restricted to such one that can be dissolved through etching. Therefore, this presents great limitation as to the choice of material for use as substrate.
Further, since the surface of the element on the substrate side after the substrate is separated is completely flat, positioning of the mask is quite difficult when the surface is processed to form an air bearing surface through photoengraving process. In general, a groove is formed about 10 .mu.m deep to form the air bearing surface. Therefore, it is necessary for the resist as a mask to be 10 .mu.m or more thick to form the groove through ion beam etching, thus making it hard to position the mask by recognizing the differences in index of reflection of the surface material (magnetic core, gap, protecting film against the sliding motion).